Identifier

Author

Degree

Doctor of Philosophy (PhD)

Department

Plant, Enviromental and Soil Sciences

Document Type

Dissertation

Abstract

Prickly sida (Sida spinosa L.) is widely distributed in the southern U.S. and is a troublesome weed in many agronomic crops. In northeastern Louisiana on silty clay loam and clay soils, prickly sida seedling emergence began in early March when soil temperature reached 13.8 C and ceased in mid-October. Seasonal peaks in emergence were associated with rainfall events and variability in prickly sida emergence was observed between soil types and years. Total emergence was as high as 3,000 prickly sida plants m-2. In shade studies, prickly sida was able to emerge and persist under a heavy shade environment and to produce a significant amount of seed when exposed to both increasing and decreasing shade levels as the growing season progressed. Under a season-long 30% shade environment, around 3,000 prickly sida seed were produced per plant. With exposure to 90% shade in the early season followed by a gradual decrease in shade to full sun, total seed production was around 8,100 seed per plant. In a weed control programs study, late season prickly sida control was 93% when glyphosate was applied both at-planting in late April/early May and postemergence (POST) in mid-May/late June. Soybean yield was increased an average of 10% when the residual herbicides chlorimuron-ethyl and tribenuron-methyl were applied with glyphosate plus 2,4-D preplant in mid-March compared with glyphosate plus 2,4-D alone. Yield was equivalent when glyphosate or glyphosate plus the residual herbicides flumioxazin, chlorimuron-ethyl, and thifensulfuron-methyl were applied at-planting and averaged approximately 25% greater than when no herbicide was applied at-planting. Application of 2,4-D or glyphosate plus 2,4-D to prickly sida reduced total seed production 78% compared with glyphosate alone. Herbicide treatments most effective for control of prickly sida present after crop harvest included diuron and linuron applied with glufosinate, paraquat, or glyphosate (75 to 85% control); diuron, atrazine, or 2,4-D ester applied with paraquat (74 to 77%); and 2,4-D ester and dicamba applied with glyphosate (75%).